Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
Recently, spread of personal information protection and My-Number requires improvement of secrecy of confidential information on a printed matter. From this aspect, when print data includes confidential information desired not to be seen by others, the information is masked to be kept secret. For example, there has been proposed a technique where, when a document is retrieved by a scanner, a part to be kept secret in the document is preliminarily marked with a specific color so as to print the part marked with the specific color with a black painting. On the other hand, there has been proposed another technique where keywords to be kept secret are registered in a dictionary and, when print data includes a keyword found to be matched, a part indicating the keyword is blotted out.